Leonard Joseph Cariou is a Canadian stage actor, singer and stage director. He gained prominence for his portrayal of Sweeney Todd in the original cast of Stephen Sondheim's musical Sweeney Todd: The Demon Barber of Fleet Street (1979) alongside Angela Lansbury for which he won the Tony Award for Best Actor in a Musical. He also received Tony nominations for his roles in the Betty Comden and Adolph Green musical Applause (1970), and the Sondheim musical A Little Night Music (1973).

Applause is a musical with a book by Betty Comden and Adolph Green, lyrics by Lee Adams, and music by Charles Strouse. The musical is based on the 1950 film All About Eve and the short story on which the movie is based, Mary Orr's "The Wisdom of Eve". The story centers on aging star Margo Channing, who innocently takes a fledgling actress under her wing, unaware that the ruthless Eve is plotting to steal her career and her man.